Eye-fatigue reduction system for head-mounted displays

ABSTRACT

Embodiments include method, systems and computer program products for reducing eye-fatigue for users of binocular head-mounted displays. Aspects include displaying a content item by a display device of the binocular head-mounted display and calculating an estimated eye-fatigue of the user of the binocular head-mounted display. Based on a determination that the estimated eye-fatigue of the user exceeds a threshold level, aspects also include modifying the content item, by the processor, to encourage the user to take an eye-fatigue reduction action and displaying the modified content item by the display device of the binocular head-mounted display.

BACKGROUND

The present disclosure relates to eye-fatigue reduction and morespecifically, to methods, systems and computer program products forreducing eye-fatigue for users of head-mounted displays.

Head-mounted displays (HMDs) are a type of display device that is wornon the head of a user. HMDs typically include a display device andassociated optics that are disposed near the user's eyes. In general,HMDs are configured to show stereoscopic imagery, which is an image thatcreates an impression of depth to the user. A binocular HMD is aparticular type of HMD that is configured to display a different imageto each eye of the user. HMDs can be used to create a remarkable senseof visual immersion and 3D stereoscopic depth. As a result, the use ofhead-mounted displays is projected to grow in popularity. The virtualreality applications for HMDs are many including, but not limited to,human research, education, engineering and scientific visualization,training, simulations, gaming, video display and the like.

One drawback to using a HMD is that the display and optics are disposedclose to the user's eyes and using the HMD for an extended period oftime can cause the user to experience eye-fatigue.

SUMMARY

In accordance with an embodiment, a method for reducing eye-fatigue forusers of binocular head-mounted displays is provided. The methodincludes displaying a content item by a display device of the binocularhead-mounted display and calculating an estimated eye-fatigue of theuser of the binocular head-mounted display. Based on a determinationthat the estimated eye-fatigue of the user exceeds a threshold level,aspects also include modifying the content item, by the processor, toencourage the user to take an eye-fatigue reduction action anddisplaying the modified content item by the display device of thebinocular head-mounted display.

In accordance with another embodiment, an eye-fatigue reduction systemthat includes a processor in communication with one or more types ofmemory and a user display. The processor is configured to receive acontent item from the memory, display the content item by the displaydevice of the binocular head-mounted display and calculate an estimatedeye-fatigue of the user of the binocular head-mounted display. Based ona determination that the estimated eye-fatigue of the user exceeds athreshold level, the processor is configured to modify the content itemto encourage the user to take an eye-fatigue reduction action anddisplay the modified content item by the display device of the binocularhead-mounted display.

In accordance with a further embodiment, a computer program product forreducing eye-fatigue for users of binocular head-mounted displaysincludes a non-transitory storage medium readable by a processingcircuit and storing instructions for execution by the processing circuitfor performing a method. The method includes displaying a content itemby a display device of the binocular head-mounted display andcalculating an estimated eye-fatigue of the user of the binocularhead-mounted display. Based on a determination that the estimatedeye-fatigue of the user exceeds a threshold level, aspects also includemodifying the content item, by the processor, to encourage the user totake an eye-fatigue reduction action and displaying the modified contentitem by the display device of the binocular head-mounted display.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram an binocular head-mounted display device inaccordance with an exemplary embodiment;

FIG. 2 is a block diagram illustrating another binocular head-mounteddisplay device in accordance with an exemplary embodiment;

FIG. 3 is a flow diagram of a method for reducing eye-fatigue for a userof a binocular head-mounted display device in accordance with anexemplary embodiment; and

FIG. 4 is another flow diagram of a method for reducing eye-fatigue fora user of a binocular head-mounted display device in accordance with anexemplary embodiment.

DETAILED DESCRIPTION

In accordance with exemplary embodiments of the disclosure, methods,systems and computer program products for reducing eye-fatigue for usersof binocular head-mounted displays are provided. In exemplaryembodiments, a binocular head-mounted display (HMD) is configured tocalculate an eye-fatigue level of a user of the HMD and to responsivelyalter the content being shown to the user to encourage the user to takean eye-fatigue reduction action. In exemplary embodiments, theeye-fatigue level of the user can be calculated based on a variety ofmetrics that include, but are not limited to, duration of use of theHMD, characteristics of the content displayed by the HMD,characteristics of the eyes of the user of the HMD, or the like. Inexemplary embodiments, the eye-fatigue reduction action can include theuser changing a depth of the user's vision (i.e., focusing their visionon an object that appears to be far away), blinking, or the like. Inexemplary embodiments, the HMD may be used in to create a virtualreality experience that can be used for gaming, educational settings,worker training, etc.

In exemplary embodiments, the content being shown to the user is alteredin a manner that encourages a user to focus on what appears to be afar-away object. For example, a stereoscopic depth can be changed forone or more pieces of on-screen content. In this way, vergence musclesin the eyes may be relaxed and allowed to recover from their fatigue byconstant vergence eye movements. A vergence is the simultaneous movementof both eyes in opposite directions to obtain or maintain singlebinocular vision.

When a person looks at an object, their eyes must rotate around avertical axis so that the projection of the image is in the center ofthe retina in both eyes. To look at an object closer by, the eyes rotatetowards each other (convergence), while for an object farther away theyrotate away from each other (divergence). Exaggerated convergence iscalled cross eyed viewing (focusing on the nose for example). Whenlooking into the distance, the eyes diverge until parallel, effectivelyfixating the same point at infinity (or very far away). Vergencemovements are closely connected to accommodation of the eye. Undernormal conditions, changing the focus of the eyes to look at an objectat a different distance will automatically cause vergence andaccommodation, sometimes known as the accommodation-convergence reflex.

In general, viewing a distant object, with parallel eye conditions,allow muscles in the eyes to relax, which is why periodic distantviewing is advised when working at a computer terminal. In a virtualreality environment produced by a HMD, the binocular nature of thesystem also causes vergence eye movements which may be detected. Distantviewing may then be not only advised, but directly produced by changingthe objects' distance in the display.

Referring to FIG. 1, there is shown a block diagram of an embodiment ofa binocular head-mounted display 100. As illustrated, the binocularhead-mounted display 100 includes a processor 102 that is configured todisplay a content item on a display device 108. In exemplaryembodiments, the display device 108 is a binocular HMD that isconfigured to create a stereoscopic version of the content item. Theprocessor 102 is communicatively coupled to a memory 106 that is used tostore a content item that will be displayed on the display device 108.In exemplary embodiments, the binocular head-mounted display 100 mayalso include one or more sensors 104 that are communicatively coupled tothe processor 102. In exemplary embodiments, the sensors 104 mayinclude, but are not limited to, an accelerometer, light sensors (suchas a photodiode), a gyroscope, electrodes or the like. In exemplaryembodiments, the processor 102 is configured to determine an eye-fatiguelevel of the user of the HMD 100 based on information received from thesensors 104 and from information regarding the content item beingdisplayed.

Referring now to FIG. 2, there is shown a binocular head-mounted display200 in accordance with another embodiment. As illustrated, the binocularhead-mounted display 200 includes a processing system 202 that isconfigured to display a content item on a display device 208. Theprocessing system 202 is communicatively coupled to a memory 206 that isused to store a content item that will be displayed on the displaydevice. In exemplary embodiments, the binocular head-mounted display 200may also include one or more sensors 204 that are communicativelycoupled to the processing system 202. In exemplary embodiments, thesensors 204 may include, but are not limited to, an accelerometer, lightsensors (such as a photodiode), a gyroscope, or the like. The HMD 200also includes a camera 203 that is configured to monitor the eyes of theuser of the HMD.

In exemplary embodiments, the processing system 202 includes a fatiguedetection module 210 and a content modification module 212. The fatiguedetection module 210 is configured to receive video of the user's eyesfrom the camera 203 and to analyze one or more characteristics of theeyes to determine an eye-fatigue level of the user of the HMD 200. Thefatigue detection module 210 is also configured to receive inputs fromthe one or more sensors 204 that can also be used to determine aneye-fatigue level of the user of the HMD 200. The content modificationmodule 212 is configured to modify content items to be displayed to theuser to insert, or modify, objects in the content item to encourage theuser to take a fatigue reduction action.

In exemplary embodiments, the processor is a hardware device forexecuting hardware instructions or software, particularly that stored ina non-transitory computer-readable memory (e.g., memory). Processor canbe any custom made or commercially available processor, a centralprocessing unit (CPU), a plurality of CPUs, a semiconductor basedmicroprocessor (in the form of a microchip or chip set), or generallyany device for executing instructions. Processor can include a memorycache, which may include, but is not limited to, an instruction cache tospeed up executable instruction fetch, a data cache to speed up datafetch and store, and a translation lookaside buffer (TLB) used to speedup virtual-to-physical address translation for both executableinstructions and data.

In exemplary embodiments, the memory can include random access memory(RAM) and read only memory (ROM). The RAM can be any one or combinationof volatile memory elements (e.g., DRAM, SRAM, SDRAM, etc.). ROM caninclude any one or more nonvolatile memory elements (e.g., erasableprogrammable read only memory (EPROM), flash memory, electronicallyerasable programmable read only memory (EEPROM), programmable read onlymemory (PROM), tape, compact disc read only memory (CD-ROM), disk,cartridge, cassette or the like, etc.). Moreover, memory 106 mayincorporate electronic, magnetic, optical, and/or other types ofnon-transitory computer-readable storage media.

The instructions in memory may include one or more separate programs,each of which comprises an ordered listing of computer-executableinstructions for implementing logical functions. In one example, theinstructions in memory 106 may include a suitable operating system thatis configured to control the execution of other computer programs andprovides scheduling, input-output control, file and data management,memory management, video generation and modification and communicationcontrol and related services.

In exemplary embodiments, the display device can include one or moredisplays and optics associated therewith. The displays can include aliquid crystal display (LCD), light emitting diode (LED) display,organic light emitting diode (OLED) display or any other known type ofdisplay. In exemplary embodiments, the display device may be removablyaffixed to the HMD. For example, the display device may be a display ofa smartphone that is configured to be selectively disposed in the HMD.Likewise, one or more of the processor, memory, sensors and camera mayalso be removably affixed to the HMD. For example, the processor, memoryand sensors may be disposed in a smartphone that is configured to beselectively disposed in the HMD.

Referring now to FIG. 3, a flow diagram of a method 300 for reducingeye-fatigue of a user of a binocular head-mounted display in accordancewith an exemplary embodiment is shown. As shown at block 302, the method300 includes displaying a content item by a binocular head-mounteddisplay. Next, as shown at block 304, the method 300 includescalculating an estimated eye-fatigue of the user of the binocularhead-mounted display. In exemplary embodiments, the estimatedeye-fatigue of the user can be calculated based on a variety of factorsthat can include, but are not limited to, one or more of: a duration ofuse of the head mounted display; a mean stereoscopic depth of object inthe content item; a standard deviation of the stereoscopic depth ofobjects in the content item; movement of the user's head as determinedby an accelerometer or gyroscope in the HMD; brain activity of the useras monitored by one or more electrodes in the HMD; or the like.

Continuing with reference to FIG. 3, the method 300 also includesdetermining if the estimated eye-fatigue of the user exceeds a thresholdlevel, as shown at decision block 306. In exemplary embodiments, thethreshold level is determined based on a user profile of the user. Theuser profile includes a plurality of threshold values of eye-fatiguelevels that can be selected based on personal information of the user,such as age, gender, medical conditions, etc. In exemplary embodiments,the plurality of threshold values of eye-fatigue levels stored in theuser profile may be obtained based on statistics collected from a largepopulation sample. Next, as shown at block 308, the method 300 includesmodifying the content item to encourage the user to take an eye-fatiguereduction action. In exemplary embodiments, the eye-fatigue reductionaction includes one or more of focusing on a specific object in themodified content item and blinking. The method 300 also includesdisplaying the modified content item by the display device of thebinocular head-mounted display, as shown at block 310.

Referring now to FIG. 4, a flow diagram of another method 400 forreducing eye-fatigue of a user of a binocular head-mounted display inaccordance with an exemplary embodiment is shown. As shown at block 402,the method 400 includes displaying a content item by a binocularhead-mounted display. Next, as shown at block 404, the method 400includes monitoring a characteristic of the eyes of the user of the HMD.The method 400 also includes calculating an estimated eye-fatigue of theuser of the binocular head-mounted display based, at least in part, onthe monitored characteristic. In exemplary embodiments, the estimatedeye-fatigue of the user can be calculated based on measurements of oneor more characteristics of the user's eyes. For example, the headmounted display may use one or more cameras to observe the user's eyesand to measure characteristics of the user's eyes, such as a diameter ofeach pupil and a frequency and amount of change in the diameter of thepupils. In addition to the monitored characteristic of the user's eyesthe estimated eye-fatigue of the user can be calculated based on avariety of factors that can include, but are not limited to, one or moreof: a duration of use of the head mounted display; a mean stereoscopicdepth of objects in the content item; a standard deviation of thestereoscopic depth of objects in the content item; movement of theuser's head as determined by an accelerometer or gyroscope in the HMD;brain activity of the user as monitored by one or more electrodes in theHMD; or the like.

Continuing with reference to FIG. 4, the method 400 also includesdetermining if the estimated eye-fatigue of the user exceeds a thresholdlevel, as shown at decision block 408. In exemplary embodiments, thethreshold level is determined based on a user profile of the user. Theuser profile includes a plurality of threshold values of eye-fatiguelevels that can be selected based on personal information of the user,such as age, gender, medical conditions, etc. In exemplary embodiments,the plurality of threshold values of eye-fatigue levels stored in theuser profile may be obtained based on statistics collected from a largepopulation sample. Next, as shown at block 410, the method 400 includesmodifying the content item to encourage the user to take an eye-fatiguereduction action. In exemplary embodiments, the eye-fatigue reductionaction includes one or more of focusing on a specific object in themodified content item and blinking. The method 400 also includesdisplaying the modified content item by the display device of thebinocular head-mounted display, as shown at block 412.

In exemplary embodiments, modifying the content item can includegenerating an object in the content item that has stereoscopic depththat is greater than a fixed distance. For example, if the content itemis a video game, modifying the content item may include inserting anobject into the video game that has a stereoscopic depth that is greaterthan an average stereoscopic depth of the objects in the video game. Inone embodiment, the content item is configured to have a stereoscopicdepth that makes the inserted item appear to be at least twice theaverage stereoscopic depth of the objects in the video game. Inaddition, modifying the content may include taking one or more actionsto encourage the user to focus on the inserted object. In exemplaryembodiments, by changing the user's focus to an inserted object thatappears to be far away, the eye-fatigue of the user can be reduced.

In exemplary embodiments, the objects may be advertisements or itemsthat are selected to get the attention of a user. The system may beconfigured to learn what types of objects a user is more likely to payattention to and look at, according to various cohorts (a person withAutism, a student, an adult, etc.) and based on user profile. In oneembodiment, the object may be a message that appears in the distancethat indicates a user should blink, which tends to reduce dry eyeproblems. This serves a dual purpose of having a user not always gazingat close objects but also inducing a blink, which a user may actuallyappreciate if his or her eyes become less fatigued in the long run. Inone embodiment, such messages may appear on “blimps” or written in thesky by graphical representations of air planes. In exemplaryembodiments, a user may be rewarded when he or she changes their focusto such a message.

The system may learn what stimuli (objects), and what distances are mosteffective in reducing fatigue for particular users. In exemplaryembodiments, the system may be adapted to differentially apply differentdistances to stare at, dependent on a user's condition or tendency: Inexemplary embodiments, the systems can detect Strabismus and Esotropiaand can alter the display device to accommodate users with theseconditions. Strabismus is a vision disorder in which the eyes don't lookin exactly the same direction at the same time. Esotropia is a form ofstrabismus, or “squint,” in which one or both eyes turns inward.Strabismus may cause amblyopia due to the brain ignoring one eye.

The most extreme forms of vergence eye movements involve looking atone's own nose, which typically causes the eye to become crossed. Ingeneral, viewing beyond the nose creates a blurred image of the noseduring all viewing conditions a human with a normal sized noseencounters. However, this reference of the blurred nose is absent incurrent HMD simulated environments. Accordingly, in one embodiment, thecontent item to be displayed by the HMD and be altered to include ablurred nose to restore the reference, realism, and possibly a means toencourage more natural vergence eye movements.

In exemplary embodiments, one or more characteristics of a user can beentered into a user profile or they can be inferred by the type ofcontent items that they view, such as the types of movies the userwatches or the type of games the user plays. In addition, the types ofobjects that are likely to draw the attention of a specific user can betracked via usage of the HMD and saved in the user profile. For example,the system can determine which objects a user pays attention to basedeye-tracking, a history of responding to prompts on such objects, etc.Thus, the system can be configured to learn one or more characteristicsof the user and can use this information to determine when his eyes areestimated to be tired (or, for example, he has been staring at nearobjects to far objects over time period T in a ratio of 10:1). Based onthe determination that the user is likely experiencing eye-fatigue, thesystem will coax the user to look at an object that is likely to get hisattention at an appropriate stereoscopic depth. For example, ifT(near)/T(far)>10 for the past half hour, then trigger the insertion ofan object, estimated to catch the user eyes, that is far away in thesense of eye gaze characteristics within an HMD.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A computer program product for reducingeye-fatigue for a user of a binocular head-mounted display, the computerprogram product comprising: a non-transitory storage medium readable bya processing circuit and storing instructions for execution by theprocessing circuit for performing a method comprising: displaying acontent item by a display device of the head-mounted display;calculating an estimated eye-fatigue of the user of the binocularhead-mounted display; based on a determination that the estimatedeye-fatigue of the user exceeds a threshold level, modifying the contentitem to encourage the user to take an eye-fatigue reduction action thatincludes inserting an object into the content item having a stereoscopicdepth that is greater than a fixed distance; and displaying the modifiedcontent item by the display device of the binocular head-mounteddisplay.
 2. The computer program product of claim 1, wherein theestimated eye-fatigue of the user is calculated based on measurements ofone or more characteristics of the user's eyes.
 3. The computer programproduct of claim 1, wherein modifying the content item includesinserting a reference object into the content item that is visibleduring use of the binocular head-mounted display.
 4. The computerprogram product of claim 1, wherein the fixed distance is determined tobe at least twice a mean stereoscopic depth of objects in the contentitem.
 5. The computer program product of claim 3, wherein the referenceobject is a rendition of a nose and wherein the reference object isinserted in a center of a field of view of the content item.
 6. Thecomputer program product of claim 1, wherein the estimated eye-fatigueof the user is calculated based on duration of use of the binocular headmounted display.
 7. The computer program product of claim 6, whereinestimated eye-fatigue of the user is calculated based on a meanstereoscopic depth of objects in the content item and a standarddeviation of the stereoscopic depth of the objects content item.
 8. Thecomputer program product of claim 1, wherein the eye-fatigue reductionaction includes one or more of focusing on the object inserted in themodified content item and blinking.
 9. A system for reducing eye-fatigueof a user of a binocular head-mounted display device, the display devicecomprising: a processor in communication with a memory and a displaydevice, the processor configured to: receive a content item from thememory; display the content item by the display device of the binocularhead-mounted display; calculate an estimated eye-fatigue of the user ofthe binocular head-mounted display; based on a determination that theestimated eye-fatigue of the user exceeds a threshold level, modify thecontent item to encourage the user to take an eye-fatigue reductionaction that includes inserting an object into the content item having astereoscopic depth that is greater than a fixed distance; and displaythe modified content item by the display device of the head-mounteddisplay.
 10. The system of claim 9, wherein the estimated eye-fatigue ofthe user is calculated based on measurements of one or morecharacteristics of the user's eyes.
 11. The system of claim 9, whereinmodifying the content item includes inserting a reference object intothe content item that is visible during use of the binocularhead-mounted display.
 12. The system of claim 9, wherein the objectinserted into the content items is selected based on a determination ofwhat type of object the user is likely to pay attention to, where thedetermination is based on one or more characteristics of the userretrieved from a user profile.